1. Field of the Invention
This invention relates to a beneficiation process for upgrading mined oil shale prior to retorting for recovery of the oil.
2. Description of the Prior Art
Large deposits of oil shale are found in many locations throughout the world, and extensive efforts have been undertaken to develop oil shale as a source of hydrocarbon products. The term "oil shale" is widely used to refer to a layered sedimentary formation containing an organic material known as kerogen which may be decomposed by heating to produce gaseous and liquid hydrocarbon products. Such processing of the oil shale may be conducted in place in the deposit (in situ) or the oil shale may be mined by conventional mining methods and the oil shale ore processed by retorting on the surface. In such retorting, particles of mined oil shale are heated over a period of time to an appropriate temperature of yield gaseous and liquid hydrocarbon fractions. Two examples of such retorts and retorting processes are those described in U.S. Pat. Nos. 3,821,353, and 4,133,741 granted to Weichman and Knight et al. respectively.
Because of the high temperatures required in known retorts and retorting processes for obtaining hydrocarbon values from oil shale, and the resultant need for large amounts of energy to provide such heat, it is desirable to retort as little oil shale as possible to obtain each gallon of oil. To accomplish a reduction in the amount of heat required to retort oil shale, others have developed processes for the beneficiation of oil shale.
Such a process is described in U.S. Pat. No. 4,257,878 which was granted to Fishback et al. in which oil shale is beneficiated by increasing the oil content of the clay-bearing oil shale ore by subjecting the oil shale ore to an aqueous medium, agitating to disintegrate at least a portion of the clay, and separating the disintegrated clay from the remaining oil shale to yield an oil shale having a greater amount of recoverable hydrocarbon values per ton than the unprocessed oil shale ore.
Moudgil et al. disclosed in U.S. Pat. No. 4,169,045 a method for the separation of shale from run of mine (ROM) shale containing particles of shale and refuse, which comprised conditioning the ROM shale with a coupling agent capable of selectively coating the kerogen hydrocarbons in the particulate shale to the substantial exclusion of coating the non-hydrocarbonaceous refuse, which coupling agent was at least one carbolic acid, preferably containing from about five to about twenty-eight carbon atoms and a ketone. Combined with the coupling agent was a fluorescent dye in a quantity sufficient to make the coated particles of shale fluoresce upon excitation to a degree sufficient to distinguish the coated shale particles from the substantially non-coated refuse.
Fahlstrom teaches a method for treating shales in U.S. Pat. No. 4,176,042. Here, kerogen-containing shale is crushed and comminuted to a fineness sufficient to free kerogen and any sulphides present in said shale. To enable the shale to be finely-divided more readily, the crushed shale is subjected to a leaching treatment prior to final comminution thereof. Fahlstrom also taught the use of a density-separation process where a non-polar, water immiscible liquid was used. This liquid had a density of from about 1.3-1.5.
Rosar et al. via U.S. Pat. No. 3,973,734 disclosed a froth flotation method for separation of sodium compounds, principally nahcolite, dawsonite, trona, related authigenic sodium ores, and corresponding sodium compounds including sodium carbonate and sodium bicarbonate, from kerogen-type organics-containing rock, by use of sodium carbonate and/or sodium bicarbonate-containing brines having a basic pH ranging above about 7.0, preferably about 8.0-12.0, and recovering a sodium compound-rich fraction as a non-float portion and an organics-rich fraction as a float portion. Frothers, froth control agents and collection agents may be used separately or in combination. Single or multiple-stage flotation, with cleaning, conditioning, scavenging, reflotation, and combining of products might also be used. Feed ore end products may be screened to abrate the head or product assay. By this method, raw or retorted oil shale may be separated from sodium minerals and compounds obtained therein.
B. M. Moudgil and N. Arbiter have given a comprehensive overview regarding oil shale beneficiation in their article entitled "Oil Shale Beneficiation for Above Ground Retorting." This article appeared in Mining Engineering at pages 1336-38 (Sept. 1982).
Applicant in the present invention has determined that oil shale can be enriched and the amount of shale oil recovered can be optimized by controlling the size of the particles for retorting purposes.
Utilizing Applicant's invention results in lower raw oil shale processing costs and lower costs in retorting the oil shale. These lower costs result from energy savings during the processing and retorting of raw oil shale.